The Washtenaw County Health Department announced Thursday that after an extensive investigation, the source of the E.coli contamination was traced to lettuce sold by an Ohio distributor. Freshway Foods of Sidney, Ohio, recalled lettuce sold in 23 states and the District of Columbia because of the outbreak that made at least 19 people sick.

The U-M supplier for food served in residence halls did not purchase any lettuce from Freshway Foods, said Sandy Lowry, associate director of housing dining services.

The county health department said it had determined that at least one local establishment has received the contaminated lettuce. That led to more than 20 people becoming ill with symptoms consistent with E.coli. Nine of those cases have been confirmed.

Most of those who became ill locally were U-M students. In fact, the first reports of the illness came from the U-M.

“The original notification of a possible outbreak (in early April) came from University Health Service when we reported to the county health department a series of 10 U-M students reporting similar symptoms,” said Dr. Rob Ernst, UHS medical director.

The county health department handled the confirming tests on the students and others who became ill. All of the students recovered.

Freshway Foods said over the weekend the tainted lettuce had been traced to a farm in Yuma, Ariz.